Reaction-turbine jet rotors use the torque from the thrust of offset jets to drive the rotation of a jetting head. Fluids pumped through these tools may include water, a water and nitrogen mixture, carbon dioxide, concentrated acid, and solvents. Reaction-turbines generate relatively low torque, so the bearings and seals must exhibit a low static friction to ensure reliable startup. The dynamic seal friction is always less than the startup friction. The torque required to reliably start the rotor is therefore typically substantially higher than the seal and bearing frictional torque. Therefore, once the startup friction is overcome, the rotors will speed up to near the runaway speed, which is determined by the tangential velocity component of the jet. The runaway speed is typically relatively high, and unfortunately, the jet effectiveness at these relatively high speeds is relatively low. High rotary speed also causes premature wear of rotor seals and bearings. Similar problems are encountered with turbine motors used for drilling. High torque turbine motors provide good drilling performance, but tend to over-speed when the bit is off bottom and not generating drag.
A variety of braking mechanisms have been developed to govern the rotary speed of a jet rotor using a reaction turbine drive. These braking mechanisms include friction speed governors, magnetic eddy current speed governors, and viscous speed governors. Each of these speed governor mechanisms have limitations at high temperature, in high-pressure multiphase flows, and in corrosive fluid environments (particularly concentrated acid environments). Axial flow turbine speed governors (such as those described in U.S. Pat. No. 3,278,040) employ vertical axial flow stators and rotors with a torque curve that increases from zero at stall, to a level that balances the torque generated by the drive section of the turbine. The brake/speed governor torque increases linearly with speed.
It would be desirable to provide a hydrokinetic speed governor of simple and compact design, which exhibits a torque curve that increases as the square of rotary speed, to provide improved speed control. It would further be desirable to provide such a hydrokinetic speed governor mechanism that can be readily constructed from a variety of corrosion-resistant materials, to provide a general speed governing mechanism for use in reaction turbine rotors employed in rotary jetting tools and in axial flow turbine motors used for drilling. Preferably, such a hydrokinetic speed governor mechanism should be configured for use with any almost fluid, including liquids, gases, or mixtures of liquids and gases.